A&A 376, L1-L4 (2001)
Water in K and M giant stars unveiled by ISOT. Tsuji
Institute of Astronomy, The University of Tokyo, Mitaka, Tokyo 181-0015, Japan
(Received 29 May 2001 / Accepted 11 July 2001 )
Based on the spectra obtained with Infrared Space Observatory, ISO, we detected the 6.3 m bands of water in the late K giant Aldebaran ( Tau) and several early M giant stars (between M0 and M3.5), which have been deemed to be too warm for tri-atomic H2O molecule to reside in their photospheres. The water column densities range molecules cm-2 in our sample of K and M giant stars and the excitation temperatures are 1500 K or higher. Thus, the water bands are not originating in cool stellar winds either. The presence of water in the K and early M giant stars was quite unexpected from the traditional picture of the atmosphere of the red giant star consisting of the photosphere, hot chromosphere, and cool wind. We confirm that a rather warm molecule forming region should exist as a new component of the atmosphere of red giant stars and that this should be a general phenomenon in late-type stars.
Key words: infrared: stars -- molecular processes -- stars: atmospheres -- stars: chromospheres -- stars: individual: Tau, And, Cet, Peg, Cru -- stars: late-type
© ESO 2001